When buying used phones off of eBay, Craigslist, or the like, a primary concern of anyone purchasing CDMA devices (Verizon, Sprint, Boost Mobile, Virgin Mobile, etc.) is the status of the phone's ESN (electronic serial number). If a device's ESN is registered as "banned" on its carrier because it has been listed as stolen or is attached to an unpaid account, then that phone cannot be activated on said carrier. Thus, the phone is either useless or has to be activated on a pre-paid carrier, which is generally not all that desirable and drastically decreases a device's worth.